[67.09] Velocity ion imaging measurements of product velocities and branching ratios in the photodissociation of CS2.

W. M. Jackson, D. Xu, J. Huang (University of California, Davis)

The velocity distribution of daughter products produced by
photodissociation is an important parameter for determining
their progenitors. Spatial profiles of cometary emissions
are usually analyzed with the Haser or the Festou vector
models, which gives a parameter called the scale length,
\gamma. The scale length is defined as the product of the
velocity of the species in the comet, u, times the
photochemical lifetime, \tau. This later quantity is the
inverse of the integral over all solar wavelengths of the
absorption coefficient of the parent times the solar flux.
The parent of the fragments can be determined from the
photochemical lifetime if the recoil velocity,v,is known.
This recoil velocity can then be combined with the gas flow
velocity to determine the cometary velocity of the species.

A pulsed supersonic molecular beam apparatus combined with a
velocity ion imaging is used to determine the identity and
velocity distributions of the daughters produced by
photodissociation. The CS2 is studied in its primary
photodissociation regime between 193- 202 nm that produces
sulfur atoms in the 3P and 1D electronic states.
The recoil velocity and branching ratios of the two
different states of the sulfur atom atoms that are produced
has been determined. Combining this information with the
solar photochemical rate constants for this wavelength
region allow us to determine an average recoil velocity for
cometary sulfur atoms produced by solar photolysis of
cometary CS2. The implication of these results will be
discussed.

This work was supported by the Chemistry Division of the
National Science Foundation (NSF) (Grant No. CHE-0100965)
and the Planetary Atmosphere program NASA (Grant No.
NAG5-12124).